feat: add LazyPartition trait for LazyMemoryExec, migrate generate_series to partitions

[ethan-tyler]

Which issue does this PR close?

• Closes Simplify LazyMemoryExec with SendableRecordBatchStream #13614

Rationale for this change

LazyMemoryExec currently uses generator closures (LazyBatchGenerator) as its partition interface. This replaces with a LazyPartition trait that gives partitions a proper abstraction while keeping the old generator path working through a legacy adapter.

generate_series/range are migrated to native LazyPartition as the first consumer. Proto roundtrip is updated to handle both native and legacy forms.

What changes are included in this PR?

• LazyPartition trait as the native partition interface for LazyMemoryExec
• LazyBatchGeneratorPartition adapter allowing existing generator to work
• Deprecated compatibility APIs preserved: LazyMemoryExec::try_new, LazyMemoryExec::generators, GenerateSeriesTable::as_generator.
• generate_series/range migrated to native GenerateSeriesPartition
• Shared helper for generate series state construction (dedupes native and deprecated paths)
• Proto roundtrip updated for native GenerateSeriesPartition with legacy adapter fallback
• Core coop test helper updated to use LazyPartition
• Proto regression test coverage added

Are these changes tested?

yes

• cargo test -p datafusion-physical-plan lazy_memory_tests --lib
• cargo test -p datafusion-functions-table generate_series_tests --lib
• cargo test -p datafusion-proto roundtrip_generate_series --test proto_integration
• cargo test -p datafusion execution::coop --test core_integration
• cargo check -p datafusion-physical-plan -p datafusion-functions-table -p datafusion-proto -p datafusion

Are there any user-facing changes?

No. LazyBatchGenerator and existing public APIs remain available (deprecated)